It can use LaTeX or pdfroff for the PDF generation as well as some other backends that I haven't tried yet. The --pdf-engine flag lets you choose between them.
Oh, so there are some available engines on Termux? I had tried just what you did and not specifying the engine would result in an error of missing pdflatex, could you give me the whole command please? Or the packages I need to install first
I haven't switched to Quillpad because I didn't see any remarkable changes from the original Quillnote, it seems like development has stalled over there too, unfortunately.
I have tried it out now, though and, as far as I can tell, the Export option is still just to make a zip of a JSON file with the text inside, no PDF to be seen.